Screen printing apparatuses are known for applying a material (e.g. a conductive paste) on the surface of a substrate (e.g. a print tape) to form a particular printing pattern defined by a screen mask or mesh. Typically, a squeegee is pulled across the top surface of a screen mask and pushes the material applied on the screen mask passes through the pattern holes of the screen mask onto the surface of a substrate positioned below the screen mask. It is a known problem that each time a new substrate is positioned at the printing position or a new screen mask is installed in the printing apparatus, the substrate and the screen mask may not in a perfect alignment and thus resulted in an imprecise printing pattern on the substrate. Therefore, if a high printing accuracy is desired, the position of the substrate or the screen mask has to be corrected before the printing process so that the substrate and the screen mask are aligned with each other.
Many alignment methods have been introduced to improve the printing accuracy and throughput. For example, some recognisable markings are printed on the substrate or the screen mask for facilitating the alignment process. The locations of the markings are measured and compared with an expected location so that positional error can be determined and corrected. Many alignment methods are meant for large scale printing systems and hence their methods are complicated and costly to implement. Although there are simpler alignment methods which can be performed semi-auto or manually, these methods are mostly less accurate and hence not desirable.
Therefore, those skilled in art are constantly striving to devise an alignment method for a screen printing system which is simple and able to provide a high printing accuracy.